Do you like communicating? If you are reading this, then the answer is YES!! All living organisms communicate with each other in some way. We humans, use typing, speaking, and signing as methods of communication. But what if you did not have access to any of these methods of communication? This is what it is like to be a bacterium. Bacterial ways of being seem so different from ours, yet they are the majority! There are nonillions of bacteria on planet Earth– WAYYY more than there are humans or other animals. And these bacteria communicate too! That is how they swarm, or move all together as one unit.
And how do they do that, you may ask? After all, bacteria have no eyes or ears or mouth or nose! Just a peptidoglycan membrane with peptidoglycan machinery, genetic information, ribosomes, and proteins inside it. In fact, their whole lives are determined by this peptidoglycan membrane! Without it, they will just burst into the open air.
Waiiitttt… we need to take a step back. What even is peptidoglycan? You must be asking. Good question! Peptidoglycan is the material that makes up the bacterial cell wall! It is a very sturdy material made up of sugars called glycan and proteins, “peptides.” They surround the entire bacterial cytoplasm and all it contains. The peptidoglycan membrane determines the shape of the bacterial cell!
You are probably thinking that nothing can get in or out of the cell, given that the peptidoglycan membrane is so strong. But things such as nutrients for the bacterium to feed on need to be able to enter the cell, and the bacterial waste has to be able to exit. To do this, there are membrane channels– just like there are in eukaryotic cells! These membrane channels are called porins in bacteria, and they allow such things to enter and exit the cell. In addition to water and nutrients, these little chemicals called quorum sensors also enter and exit the cell. And THAT is how bacteria communicate with each other. This form of communication is called “quorum sensing” or “quorum signaling,” often shortened to QS.
QS works by the bacteria releasing tiny chemical molecules into their environment. But let’s not call them “molecules” for a second. Because, let’s be real, that sounds boring. Let’s call them what they really are: messages.
Imagine thousands of bacteria just… vibing. Each one quietly releases little chemical “notes” into the space around them. At first, it’s like whispering into a huge room where no one really hears anything. The signals are too diluted, too scattered.
But then more bacteria show up. And more. And then some more.
Now the room is getting louder and louder. Almost deafening.
At some point, the concentration of these signals gets high enough that bacteria start to “peep” them. It’s like when a party suddenly reaches that moment where everyone realizes “oh wow, there are a LOT of us here”. And that’s when things start to…change.
All at once, they just kind of switch.
Genes turn on. Behaviors begin to ACTIVATE like they are transformers. The bacteria go from being independent little cells to acting like a coordinated group. Because we roll out as a group!!
That is quorum sensing.
QS also works differently in different bacteria. A scientist by the name of Ágnes Ábrahám sought to figure out how it works in the bacterial species called Pseudomonas aeruginosa, ESPECIALLY when there are changes to the LasR protein. Now here’s where things get a little more specific—and a little more interesting.
LasR is kind of like… the group chat admin.
It doesn’t send messages, but it reads them.
When those quorum-sensing signals enter the cell (through those porins we talked about earlier), LasR binds to them. And once enough signals are bound, then BOOM. LasR activates and starts turning on genes.
So, if quorum sensing is the conversation, LasR is the one saying:
“Okay, everyone, it’s time. Let’s do this.”
Without LasR, the bacteria are basically sitting there like:
“Hello?? Is anyone talking?? I can’t hear anything???” “Bueller! Bueller!”
So yeah… pretty important.
But who exactly is P. aeruginosa? Well, to start with, this bacterium is not exactly your best friend. It’s what we call an opportunistic pathogen, which is just a fancy way of saying it takes advantage of situations where the body is vulnerable. It’s found in water and soil (which can have unstable conditions). When the bacterium infects a host and enters their bloodstream, it can lead to serious conditions like lung infections and pneumonia.
So yeah… not ideal.
But ALSO, this is exactly why scientists are obsessed with studying it and are striving to understand how to treat it more effectively. And one of the promising directions in achieving this goal is finding more effective strategies to combat the infections.
Because P. aeruginosa is really, really good at surviving. It forms biofilms (basically bacterial cities), resists antibiotics, and most importantly, it uses quorum-sensing to coordinate all of that.
So, if we can understand how it communicates, we might be able to interrupt the conversation.
And if we interrupt the conversation… we might be able to stop the infection before it even gets organized.
So picture this…
You’re a scientist, and instead of looking at a huge crowd of bacteria all at once, you decide to zoom ALL the way in.
Like… one bacterium at a time.
This is exactly what Ágnes Ábrahám and her team did. They used this tiny device called a microfluidic “mother machine” which is used to trap individual bacteria in little channels, so they could watch them divide, grow over the generations, and respond to changes over time (see Figure 1a from the paper).
Figure 1. Tracking the quorum-sensing behavior of P. aeruginosa cells in a microfluidic mother machine device during the application of different concentrations of externally added signal molecules (10 nM and 1 μM 3O-C12-HSL). (a) Schematic illustration of the microfluidic device (not scaled).
Also, check out a sneak peek from one of the two short movies from the paper! (see Supplemental Movie 1 below).
Supplemental Movie 1. Illustrates quorum signal onset and quorum decay after a 1 μM signal treatment for single-cell responses.
Then they did something clever.
Figure 4. Theoretical model of the population-level QS response. (a) Schematic diagram of the functional components used in the model. (b) The results of the numerical model (blue line: 10 nM signal molecule concentration, and red line: 1 µM signal molecule concentration) along with the measured average fluorescence intensities (grey dots: 10 nM, black dots: 1 µM). (c) Calculated concentrations of molecular species (r1, r2, r3, r4, n) included in the model (solid lines), and the concentrations of gfp genes with bound LasR-signal complex (sa, dashed line) for both signal molecule concentrations.
In order to study the QS decay at the population level, they followed another scientist’s methods (Claussen et al.) to help establish a model for looking into fluorescence responses alongside the presence or absence of the signaling molecule. In a part, they illustrated their version of the setup behind and the modifications specific to their experiment. The second part shows the measured and expected average fluorescence fluctuations over time from the onset to the decay for both signal concentrations. The last part of the figure, part c, compares how the two signal concentrations between five different strands of the bacteria affect the GFP concentrations.
So, at the core of the experiment, they gave the bacteria quorum-sensing signals… and then took them away… and then gave them back again.
Kind of like flipping a light switch on and off.
And here’s where things got weird.
When the signal was turned ON, the bacteria responded pretty quickly. They activated their quorum-sensing system, started producing proteins, and everything looked normal.
But when the signal was turned OFF…
…they didn’t just stop.
Instead, they kept going.
For hours and hours and hours…
Even though the signal molecules were gone, the bacteria stayed in that “ON” state much longer than expected.
It’s like the party ended… but everyone just kept dancing anyway.
And it gets even better (or weirder?).
Not all the bacteria behaved the same way.
Some cells responded super strongly. Others barely reacted. Even cells that came from the same “parent” cell—like literal bacterial siblings—started to behave differently over time.
So, on the individual level? Total and absolute chaos.
But when the scientists zoomed back out and looked at the whole population…
Everything smoothed out.
Most of the bacteria still ended up doing the same thing at the same time.
So somehow, this messy, unpredictable single-cell behavior turns into a coordinated group response.
And honestly, that might be the coolest part of this whole story.
Because it shows that bacteria aren’t just simple little blobs reacting instantly to their environment.
They communicate, respond with delays, show variability, and still manage to act together.
Which means quorum sensing isn’t just an ON/OFF switch.
It’s more like… a dimmer switch. With lag. And noise. And a little bit of memory.
And once you realize that bacteria can do all of that without a brain, without organs, without anything we normally associate with “thinking”…
…it kind of changes how you see them.
Not just as tiny cells. But as systems.
Works Cited:
Ábrahám, Á., Dér, L., Csákvári, E. et al. Single-cell level LasR-mediated quorum sensing response of Pseudomonas aeruginosa to pulses of signal molecules. Sci Rep 14, 16181 (2024). https://doi.org/10.1038/s41598-024-66706-6
Claussen, A., Jakobsen, T. H., Bjarnsholt, T., Givskov, M., Welch, M., Ferkinghoff-Borg, J., & Sams, T. (2013). Kinetic Model for Signal Binding to the Quorum Sensing Regulator LasR. International Journal of Molecular Sciences, 14(7), 13360-13376. https://doi.org/10.3390/ijms140713360
About the Authors:
Coming soon!
No comments:
Post a Comment